In a hierarchy of a wireless interface that conforms to an OSI reference model of a wideband-code division multiple access (W-CDMA) mobile communication system, a layer 2 (data link layer) is mainly subject to terminals interconnection and data link control that transfers data unmistakably.
Further, the layer 2 includes three sublayers of a media access control (MAC) layer, a radio link control (RLC) layer, and a packet data convergence protocol (PDCP) layer; the function unit in each of the sublayers performs individual processing.
The aspects of the processing pieces performed in the function units in the respective sublayers are in accordance with a value set in parameters in the layer 2. For example, the parameters in the layer 2 determine an upper limit of the information storage capacity of a buffer which is used in each of the processing pieces and timing at which retransmission processing is performed.
Conventionally, the parameters in the layer 2 have been set by the function unit in layer 3, which is higher in order. The function unit in layer 3 decides the type of a communication service such as speech call or information streaming and, based on a communication rate and an allowed latency time which are prescribed for that communication service, sets the parameters in the layer 2.
That is, conventionally, the layer 2 parameters of a wireless communication device in communication have been statically set beforehand based on a communication service etc. and remained a fixed value without being changed to an appropriate value even if a deterioration in state of a wireless propagation path degraded a communication situation.
FIG. 1 is a schematic diagram of a wireless communication system including base stations and mobile stations. Base stations 320, 330, 340, and 350 perform wireless communication with the mobile stations present in cells 321, 331, 341, and 351 respectively. The base stations 320, 330, 340, and 350 are each connected to a core network (CNW). Further, the base stations 320 and 330 and the base stations 340 and 350 configure the different wireless communication systems in such a configuration that those two systems may communicate with each other via the core network (CNW).
The wireless propagation path may change, for example, in a case where the mobile station 310 moves speedily or goes away from the base station 320 when the base station 320 and the mobile station 310 are communicating with each other.
Further, in a case where the mobile station 311 is communication at an edge of the cell of the base station 320 as illustrated in FIG. 1, its inbound signal interferes with signal from the neighboring base station 330 to have an influence on wireless communication in the cell 331.
In view of the above, in an IMT-2000 type S3G system that employs W-CDMA mobile communication, to reduce the interference, the base station 320 suppresses inbound transmission power of the mobile station 311. That is, the wireless propagation path between the mobile station 311 and the base station 320 that is already deteriorated at a cell edge where those stations are far away from each other becomes more deteriorated due to the power suppression function of the base station 320.
Further, if handover occurs as the mobile station 310 moves from the cell 321 into the cell 331, not-yet-arrived data that is not received by the mobile station 310 is transferred from the handover-source base station 320 to the handover-destination base station 330 in inter-station data forwarding processing. The amount of the data transferred in this case can be adjusted by changing the parameters in the layer 2; however, such adjustment has not been performed.
The prior art technologies may include, for example, Patent Documents 1 to 4.
Patent Document 1 has a description to the effect that if HARQ transmission fails, packet data is fragmented and retransmitted on the basis of wireless channel condition and whether handover has occurred.
Patent Document 2 has a description to the effect that in adaptive modulation control for changing a modulation method in accordance with CQI information denoting condition of a wireless environment, a direction in which the wireless environment changes is reflected in the CQI information to conduct adaptive modulation control.
Patent Document 3 has a description to the effect that in adaptive modulation control for changing a modulation method in accordance with CQI information denoting condition of a wireless environment, if a handover occurs, timing at which the CQI information is transmitted is changed.
Patent Document 4 has a description to the effect that if a wireless environment deteriorates, a packet-unitary transmission interval is set longer.
Patent Document 1: Japanese Patent Application Laid-Open No. 2008-118640
Patent Document 2: Japanese Laid-Open Patent Publication No. 2006-157133
Patent Document 3: Japanese Laid-Open Patent Publication No. 2006-246089
Patent Document 4: Japanese Laid-Open Patent Publication No. 2007-300509
However, if the wireless propagation path changes, a variety of transmission losses or delays occur based on values set to the layer 2 parameters. For example, even if communication errors occur consecutively owing to deteriorations in the wireless propagation path, retransmission processing continues based on the existing values set to the layer 2 parameters, so that transmission loads increase.
As for handover, for example, if handover occurs in a plurality of mobile stations simultaneously owing to movement in a train, data forwarding processing based on the existing values set to the layer 2 parameters is performed simultaneously, so that a transmission load or a delay occurs between base stations.
To solve such a problem in transmission load and delay, preferably the layer 2 parameters may be set on the basis of results of decision on the processing by the layer 3 and then dynamically changed following a change in the wireless propagation path or handover.